suboptimal code generation in strlen constant folding

[llvmbot]

Bugzilla Link	11181
Resolution	FIXED
Resolved on	Oct 19, 2011 19:34
Version	trunk
OS	All
Reporter	LLVM Bugzilla Contributor
CC	@efriedma-quic

Extended Description

target datalayout = "e-p:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-f80:32:32-v64:64:64-v128:128:128-a0:0:64"

declare i32 @​strlen(i8* noalias nocapture) nounwind readonly
@​nullstring = internal constant i8 0

define i32 @​main() {
%len = tail call i32 @​strlen(i8* @​nullstring) nounwind
ret i32 %len
}

strlen does not seem to look at the data behind @​nullstring when it does not have a specific format

[efriedma-quic]

Yes, the constant string folding is normally looking for a global more like "@nullstring = internal constant [1 x i8] zeroinitializer". This shouldn't be too hard to add, though.

[llvmbot]

Fixed in r142558. Thanks for the testcase!